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1. Field of the Invention
This invention relates to wireless communication systems, such as those including automatic retransmission and error recovery for packet oriented point-to-multipoint communication.
2. Related Art
In communication systems, messages from a sender to a receiver using a communication link are sometimes subject to sending errors, such as bit errors, unreasonable sending delay, unintended reordering, and unintended duplication of messages. For example, noise on the communication link can cause bits within messages to be incorrect, generally causing the receiver to be unable to use the message. In a wireless communication system, these problems are exacerbated by a variety of circumstances that are specific to wireless communication. For example, co-channel interference (CCI), multipath and multipoint effects, such as refraction or reflection resulting in intrasymbol interference and intersymbol interference, are often prevalent with wireless communication, and can substantially reduce the reliability of wireless communication links.
One known method in digital communication systems is to implement an automatic retransmission protocol between sender and receiver, so that the receiver acknowledges messages from the sender, and the sender re-transmits those messages not acknowledged by the receiver within a reasonable time. Known automatic retransmission protocols include several parameters, which must generally be selected in response to characteristics of the communication link, to optimize communication throughput between the sender and receiver.
One problem with application of this known method to wireless communication systems is that there are multiple physical characteristics of the wireless communication link, each which is specific to a particular combination of sender and receiver, and each of which can change substantially over relatively short time durations. These multiple physical characteristics can include characteristics of the sender's equipment or of the receiver's equipment, characteristics of objects on or near communication pathways between the sender and the receiver, and characteristics of other communications overlapping communication between the sender and the receiver. For example, the wireless communication environment can include substantial changes in wireless communication link characteristics in the time duration between sending a message and sending an appropriate acknowledgement for that message. This is particularly so for characteristics related to errors in sending information using wireless communication links, including interference such as CCI, and multipath and multipoint effects. Moreover, multiple ones of these physical characteristics can change independently of one another, and can have substantial and relatively unpredictable effects on one another.
Accordingly, selection of a single set of parameters with which to optimize automatic retransmission using a wireless communication link is virtually always suboptimal for communication among multiple senders and multiple receivers. Moreover, selection of parameters with which to optimize automatic retransmission can be subject to substantial data collection and computation; this task is not easily distributed among multiple senders and multiple receivers. Accordingly, it would be advantageous to provide a technique for automatic retransmission and error recovery for packet oriented point to multipoint communication, that is not subject to drawbacks of the known art. Preferably, in such a technique, automatic retransmission and error recovery characteristics are responsive to changes in the characteristics of the communication link between sender and receiver.